The present invention relates to a pulp stock consistency measuring device adapted to be used in a paper manufacturing machine, for example, where it is important to provide in the headbox a pulp stock of a predetermined consistency.
In particular, the present invention relates to a pulp stock consistency measuring device which is adapted to be situated in a conduit along which the stock flows with a sensing member of the device shearing the flowing pulp stock while reacting in response to engagement therewith for providing a torque which can be measured for indicating the consistency of the stock.
In accordance with the measurement of the consistency of the flowing pulp stock suitable controls will be actuated for adding to the stock a suitable diluting solution in the event that the consistency measurement indicates that the stock is too thick, or reducing the amount of diluting solution which is added to the stock in the case where the consistency measurement indicates that the pulp stock consistency is not great enough.
One of the problems encountered with consistency measuring devices of this type is that the torque measurement is undesirably affected by variations in the velocity of flow of the pulp stock, so that these variations resulting from the pulp stock velocity flow introduce errors in the measurement of the consistency of the stock.
In the paper and cardboard industry measuring devices of this type are used among others for measuring the consistency of the pulp stock, such devices being mounted in a conduit or pipe through which the stock flows and including a sensing means which shears the flowing stock. The torque actuated by the sensing means as a result of engagement between the sensing means and the flowing pulp stock serves as a basis for the consistency measurement. With respect to the state of the art reference may be made, for example, to Finnish Pat. No. 33,814. As has been indicated above, one of the problems encountered with measuring devices of this type is that the variations in the flow velocity of the pulp stock undesirably affect the results of the measurement. Attempts have been made to compensate for these effects, for example in the manner disclosed in Finnish Pat. No. 41,695.
Thus, it has been attempted in measuring devices of this type to give the sensing element a configuration according to which the extent to which the measured torque depends upon the flow velocity of the pulp stock is minimized. Thus, with this latter objective in mind the sensing element conventionally has been given the shape of a suitably curved paddle, with the paddle extending in the downstream direction with respect to the flowing stock. The plane of the blade of the paddle is conventionally perpendicular to a shaft which carries the sensing member, and a measuring mechanism measures the torque produced with respect to this shaft. By selecting in advance a suitable magnitude of the angle between the paddle blade and the direction of flow in a plane at right angles to the shaft which carries the blade, or by joining to the blade surfaces which deflect the flowing stock, it has been possible to provide a torque which is substantially independent of the flow velocity within a given flow velocity range, but this latter limited result has been achieved only with a given range of stock consistency, so that desired results can only be achieved in a manner which is dependent upon the type of fibers which are in the stock.